The present invention relates to a process for preparing xylylenediamine, comprising the steps of
ammoxidizing xylene to phthalonitrile, by contacting the vaporous product of this ammoxidation stage directly with a liquid organic solvent (quench),
removing products having a boiling point higher than phthalonitrile (high boilers) from the resulting quench solution or suspension and hydrogenating the phthalonitrile,
Xylylenediamine(bis(aminomethyl)benzene) is a useful starting material, for example for the synthesis of polyamides, epoxy hardeners or as an intermediate for preparing isocyanates.
The term “xylylenediamine” (XDA) includes the three isomers ortho-xylylenediamine, meta-xylylenediamine (MXDA) and para-xylylenediamine.
The term “phthalonitrile” (PN) includes the three isomers, 1,2-dicyanobenzene=o-phthalonitrile, 1,3-dicyanobenzene=isophthalonitrile=IPN and 1,4-dicyanobenzene=terephthalonitrile.
The two-stage synthesis of xylylenediamine by ammoxidizing xylene and subsequently hydrogenating the resulting phthalonitrile is known.
EP-A2-1 113 001 (Mitsubishi Gas Chem. Comp.) describes a process for preparing nitrile compounds by ammoxidizing corresponding carbocyclic or heterocyclic compounds, in which excess ammonia from the reaction product is recycled. Also described is the direct contacting of the vaporous product of the ammoxidation stage with a liquid organic solvent which is in particular aliphatic or aromatic hydrocarbons (paragraphs [0045] and [0046]).
EP-A2-1 193 247 and EP-A1-1 279 661 (both Mitsubishi Gas Chem. Comp.) relate to a process for purifying isophthalonitrile (IPN) and to a process for preparing pure XDA respectively, in which the phthalonitrile is synthesized by ammoxidizing xylene, and the vaporous product of the ammoxidation stage is contacted directly with a liquid organic solvent (quench). The organic solvent is selected from alkylbenzenes, heterocyclic compounds, aromatic nitriles and heterocyclic nitriles, and has a boiling point which is below that of phthalonitrile (EP-A2-1 193 247: column 4, paragraph [0018] and [0019]; EP-A1-1 279 661: columns 4-5, paragraph [0023] and [0024]).
EP-A2-1 193 244 (Mitsubishi Gas Chem. Comp.) describes a process for preparing XDA by hydrogenating phthalonitrile which is synthesized in a preceding stage by ammoxidizing xylene, in which the vaporous product of the ammoxidation stage is contacted directly with a liquid organic solvent (quench) and the resulting quench solution or suspension is fed to the hydrogenation.
Preferred organic solvents are C6-C12 aromatic hydrocarbons such as xylene and pseudocumene (column 6, paragraph [0027] and [0028]).
DE-A-21 64 169 describes, on page 6, last paragraph, the hydrogenation of IPN to meta-XDA in the presence of an Ni and/or Co catalyst in ammonia as a solvent.
Five parallel BASF patent applications each having the same application date each relate to processes for preparing XDA.